Haemoglobin

Question 1

What is required by all cells to provide ATP?

Answer 1

Oxygen is required by all respiring cells along with glucose in order to provide ATP.

Question 2

What is haemoglobin?

Answer 2

Haemoglobin is a globular protein which features a haem prosthetic (non-protein) group in the centre of each of its four subunits.

Question 3

How many oxygen molecules can each haemoglobin molecule bind to?

Answer 3

Each haemoglobin molecule can bind with up to 4 O2 molecules.

Question 4

What does dissociation or unloading mean?

Answer 4

The process by which haemoglobin releases oxygen at the tissues

Question 5

What does association or loading mean?

Answer 5

The process by which haemoglobin binds with oxygen at the lungs

Question 6

What is partial pressure?

Answer 6

Partial pressure is a measure of the concentration of a gas present. As it is a pressure it is measured in kPa.

Question 7

What is the partial pressure like in the tissues?

Answer 7

The ppO2 in the tissue capillaries is only about 5.0 kPa

Therefore, haemoglobin has a low affinity for O2 at a low ppO2 and so the oxyhaemoglobin starts to break down and releases oxygen.

Question 8

What is the partial pressure like in the lungs?

Answer 8

The partial pressure is high in the capillaries (about 13.16 kPa)

So, haemoglobin has a high affinity fr oxygen at a high partial pressure

Haemoglobin becomes fully saturated as the red blood cells pass through the pulmonary capillaries

The haemoglobin has bound its maximum amount of oxygen and is 98%+ saturated

Question 9

How does oxygen get to the tissues?

Answer 9

Oxygen unloaded/dissociates from/released (in area of lower ppO2 / in capillaries/to cells/tissues as haemoglobin has a lower affinity for oxygen for aerobic respiration

Question 10

Oxygen dissociation for adult haemoglobin - Why is the curve ‘S’ (sigmoid) shaped?

Answer 10

The shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bind to one of the sites on its four polypeptide subunits because they are closely united.

Consequently, at low partial pressures of oxygen, little oxygen binds to the haemoglobin and the gradient of the curve is shallow initially

However, binding of the first oxygen molecule changes the quaternary structure of the molecule causing it to change shape.

This change makes it easier for the second subunits to bind to oxygen.

Consequently, a small increase in the partial pressure of oxygen leads to a steeper gradient of the curve showing positive cooperativity

With the third and fourth oxygen molecules there is a reduced probability that the oxygen will find an unoccupied haem group to bind to therefore the gradient of the curve reduces and the graph flattens off.

Question 11

Q. Explain how changes in the shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin dissociation curve (3)

Answer 11

First oxygen binds to haemoglobin causing change in tertiary / quaternary structure of haemoglobin

Shape change of haemoglobin allows more O2 to bind (easily) because it uncovers another binding site
OR
Cooperative binding

Question 12

Q. The first molecule of oxygen to bind causes a change in the shape of the haemoglobin molecule. Explain why

Answer 12

At low partial pressure of oxygen, little increase in saturation as oxygen increases;

(then) rapid rise as it gets easier for oxygen to bind.

Question 13

Why does the Bohr shift occur?

Answer 13

During increased aerobic respiration, CO2 is produced

This causes a reduction in the affinity of haemoglobin for oxygen

Oxyhaemoglobin dissociates at higher oxygen concentration / partial pressure / more oxygen unloaded at the same ppO2;

Question 14

How does the Bohr shift happen?

Answer 14

CO2 from aerobic respiration forms carbonic acid in the blood which dissociates into H+ ions

Low pH / (more)H+ causes increased dissociation of oxygen from haemoglobin

Oxygen diffuses from red blood cell to tissues

Question 15

Why do mammals with a large surface area to volume ratio have an oxygen dissociation curve to the right?

Answer 15

Smaller mammal / larger SA:Vol ratio more heat lost (per unit body mass)

Smaller mammal / larger SA:Vol ratio has greater rate of respiration / metabolism

Oxygen required for respiration so (haemoglobin) releases more oxygen / oxygen released more readily / haemoglobin has lower affinity

Question 16

What is the advantage of mammals with a large surface area to volume ratio having an oxygen dissociation curve to the right?

Answer 16

At the tissues at low pp oxygen the shrew’s haemoglobin is less saturated with oxygen / has reduced affinity

Oxyhaemoglobin dissociates more readily / haemoglobin releases

oxygen more readily / more oxygen released
Allowing greater demand / respiration rate

Question 17

What does it mean if the curve shifts to the left?

Answer 17

Some species haemoglobin has a higher affinity for O2.

It becomes fully saturated at a lower ppO2 and rapidly unloads its oxygen when the haemoglobin passes into the tissues

Question 18

When animals have a curve that shifts to the right they d they have a higher metabolic rate?

Answer 18

Yes.

These are animals like cheetahs (very active) or small mice (Lose heat through a large sa:v)

In these animals:
Haemoglobin has a lower affinity for O2

So oxyhaemoglobin dissociates more readily/ haemoglobin releases O2 more readily at the same ppO2

O2 is more readily available to respiring cells